Molecular movements and translocations controlled by transition metals and signaled by light emission

Transition metals can play a detg. role in promoting oriented movements at the mol. level. Examples include the oscillation of a pendant arm in Ni(II) and Cu(II) scorpionate complexes (i.e., complexes of a tetraaza macrocycle contg. a flexible coordinating side chain), which can be relocated either on the metal center or far away from it, by varying pH. A transition metal itself can be reversibly translocated between the 2 defined compartments of a heteroditopic multidentate ligand, by taking profit (i) of a pH change (which modifies the binding tendencies of 1 compartment) or (ii) of a variation of the redox potential [which changes the oxidn. state of the metal, e.g., Fe(III)/Fe(II), Cu(II)/Cu(I)]. Examples are given in which the mol. motion [the swinging of the pendant arm in an Ni(II) scorpionate complex; the pH-driven translocation of an Ni(II) ion within an acid-sensitive 2-box system] is signaled to the outside through a net change of the fluorescent emission of a built-in anthracene fragment.